Shape memory alloys (SMA), such as nickel-titanium alloys, copper-aluminum-nickel alloys, copper-zinc-aluminum alloys, iron-manganese-silicon alloys, and the like, are metallic alloys that remember their geometry. After such alloys are deformed, they regain their original geometry by themselves during heating (one-way effect) or, at higher ambient temperatures, simply during unloading (pseudo-elasticity). This capability results from a temperature-dependent martensitic phase transformation from a low-symmetry martensite structure to a highly symmetric crystallographic austennite structure. In most shape memory alloys, a temperature change of only about 10° C. is necessary to initiate this phase change. The most common shape memory alloy, a nickel-titanium alloy, was first developed in 1962-1963 by the Naval Ordnance Laboratory, White Oak, Md., and commercialized under the trade name Nitinol (an acronym for Nickel Titanium Naval Ordnance Laboratories).
Electrical switching devices, in particular, vacuum tube electrical switching devices such as relays, switches, resettable fuses, and the like, typically employ electromechanical actuators or solenoids which are prone to failure. Complex avionic equipment often employs large numbers of such devices, thereby limiting the reliability of the equipment and aircraft. For example, high frequency (HF) antenna couplers used in aircraft communications systems employ vacuum relays for connecting the capacitors and inductors in the coupler during the tuning phase to create an appropriate impedance match to the antenna. Typical HF Antenna Couplers may employ many such relays (e.g., 30 or more). During manufacture, each relay must be carefully hand soldered and tested. Assemblies of the relays are then functionally tested. The failure of any relay in an assembly may require additional companion relays to be removed and replaced, the assembly to be reassembled, tuned and retested. In the event a vacuum relay fails in use either before or during flight of the aircraft, the HF antenna coupler must be removed from the aircraft and replaced, which may result in undesirable grounding of the aircraft. Thus, the failure of a single relay is undesirably expensive.
Consequently, it would be advantageous to provide electrical switching devices, including but not limited to, vacuum tube electrical switching devices such as relays, switches, resettable fuses, and the like, which employ actuator mechanisms formed of a shape memory alloy (SMA) for improved reliability and reduced cost.